In the manufacturing process of a silver halide light-sensitive photographic material (hereinafter may be merely called `light-sensitive material`), various process operations such as the crystal growth, ripening and coating of silver halide emulsions, slitting and cross-cutting and packaging of the coated film, and the like, are performed in a light emitted through a safelight filter which, in order to prevent the light-sensitive material from being fogged, is designed so as to reduce or intercept the light in wavelength regions to which the light-sensitive material is sensitive. The safelight is essentially required to be visually bright and to hardly fog light-sensitive materials. Both the requirements, however, are incompatible with each other, and where a light-sensitive material is handled in a conventional safelight, a gradual increase in the fog of the light-sensitive material is inevitable; even when no fog seemingly appears because of a slight amount of safelight illumination, in fact the fog potentially increases, and if the exposure of the light-sensitive material to the safelight is still further continued, then the fog will radically increase.
The safelight device, which has conventionally been used in handling light-sensitive materials, is called a `lamp house` (the safelight device is hereinafter referred to as `lamp house`), is of a construction as shown in, e.g. FIG. 5, composed of a metallic front cover 1 for fixing a safelight glass plate, a safelight glass plate 2, a metallic rear cover 3 having a reflection effect, and an incandescent lamp 4 as a light source.
Such a conventional lamp house which uses an incandescent lamp 4 as a light source is considered undesirable for practical use because if a large wattage-having incandescent lamp is used in trying to make the lamp house brighter, its generation of heat is so large that the lamp house itself becomes highly heated. Also, the conventional lap house is designed so that the light from incandescent lamp 4 is cut by safelight glass 2 into appropriate wavelength regions to which the light-sensitive material is not sensitive. The safelight glass, however, is not enough for the cutting, resulting in the shortening of the safety time of handling the light-sensitive material; this problem is more significant particularly in the case of an infrared light-sensitive material because the safelight glass 2 is unable to sufficiently cut infrared rays. In addition, in order to make the incandescent lamp 4 as a point source of light into the form of a plane, flat light, a certain spatial distance is required between the lamp and the safelight glass 2; that is, the light h as shown in FIG. 4 becomes large. Accordingly, the lamp house becomes so bulky that its installation is restricted in respect of space saving. For this reason, it is difficult for the lamp house to illuminate a limited area or to be installed in a narrow space and also to effectively illuminate only a desired area, so that the whole operation area cannot but be illuminated by the safelight, leading to the exposure of a light-sensitive material in manufacture to the safelight.
A light-sensitive material in the form of a finished product, in the stage of being practically used, is usually unpacked in a darkroom and handled again in safelight for the sake of various operations. The handling in safelight has a possibility of fogging a light-sensitive material. This is caused not only by the characteristics of the safelight used but also by the proneness of the light-sensitive material itself to be fogged. Namely, a light-sensitive material that has been exposed for a long period of time or strongly to safelight, after its completion, is prone to be fogged by the illumination of safelight in the stage of being practically used, raising a problem that shortening the allowable light-sensitive material handling time in the safelight is inevitable.
Such the problem, because the conventional safelight glass with an incandescent lamp is not enough to intercept infrared rays having a wavelength region of above 700 nanometer, is significant particularly in the case of a silver halide light-sensitive material sensitized to infrared rays. From the practical use point of view, while it goes without saying that the safelight for darkroom use should be not only visually bright but hardly fog light-sensitive materials, it is also desirable that the light-sensitive material to be used be one that permits the allowable illuminating time of the safelight in its manufacturing process to be as much long as possible.